In many aircraft intended for carrying passengers, the aircraft engines are suspended from a pylon which is itself fixed to the underside of the aircraft wing structure.
FIG. 1 schematically depicts a connection between a wing 1 of an aircraft and an engine 2, consisting of a bypass turbojet engine. This connection is afforded by means of the pylon 3 which allows the loads generated by the engine 2 to be transmitted to the structure of the aircraft and also allows fuel pipes, electrical, hydraulic and air systems to be run between the engine 2 and the wing 1 of the aircraft.
In the description that follows, the front and the rear are defined relative to a direction of forward travel F of the aircraft. In addition, the direction of the axis of rotation of the engine 2 is referred to as the longitudinal direction X, the direction running at right angles to the longitudinal direction X, in a horizontal plane, is referred to as the transverse direction Y, and the direction running at right angles to the longitudinal direction X, in a substantially vertical plane, is referred to as the horizontal direction Z. These three directions X, Y and Z are mutually orthogonal.
The engine 2 is attached to the pylon 3 by an attachment device comprising a front suspension 4, a rear suspension 5 and load-reacting links 6. This attachment device supports, on the one hand, the weight of the engine 2 and, on the other hand, the significant loads generated by the engine 2, which are applied in different directions when the engine 2 is propelling the aircraft and when the aircraft 2, through a thrust-reversal system, is slowing the aircraft.
In the engine rear suspension 5, attachment of the engine 2 to the pylon 3 is, in some aircraft, notably performed using a shackle or link connected, via spherical joints, to two substantially parallel pins each one borne by clevis mounts, one of the pins being secured to the pylon 3 and the other being secured to the engine 2.
The engine 2 may shift slightly relative to the pylon 3 according to the loadings applied by this engine. The spherical joints that connect the shackle to the two pins allow this shifting without damaging the suspension 5. However, these spherical joints also allow the shackle to pivot about an axis passing through the center of the two spherical joints, into positions in which the edges of the shackle come into contact with the cheeks of the clevis mounts bearing the pins.
Such contact between components subjected to very substantial loadings and vibrations may cause premature wearing of the shackle and/or of the clevis mounts, potentially requiring them to be replaced at closely-spaced intervals. This replacement of components of course represents a significant cost to the operators of the aircraft.